This series of ramblings is an account of my life in IC
design. It's a living document, i.e. it might change from time to time.

I went through university (1969 to 1972) on a thick sandwich course
-
the idea being that you did a year with your sponsor before university,
worked for them each summer vacation, and then did a year after
university. My sponsor was the UK Ministry of
Defence, which paid me a good salary - better than a student grant! But
their training wasn't up to much, at least until my last year, which I
spent at two
research establishments. After this I went back to my "base"
establishment
and got involved with designing thick film circuits. This was a new
in-house capability intended to show Ferranti, an early UKIC company, that we could
compete with their custom analogue IC on a
particular project. Thick film
was really quite new then and seemed to hold a lot of promise;
particularly
useful was the ability to have resistors of any value and the ability
to
trim them, not just to a specific value but also to achieve some
required
function such as a filter cut-off frequency.

After a few years I'd had enough of working for the government and
applied for anything going in the corner of England (rather
arbitrarily) south and west of Oxford. After a gruelling interview at Normalair
Garrett in Yeovil (then part of Westland helicopters),
which did not
result in a job offer, I had a more rewarding session at PyeTMC at Malmesbury. This company had been
based
in Dulwich, London, and had just moved out to the West Country.

The
Pye group was quite large, being famed especially for professional
wireless products, audio and TV, even a record
label. TMC (for Telephone Manufacturing Company)
seemed to be fairly autonomous though and was expanding fast. Its
competitive advantage was the ability to design custom ICs - at that
time very few businesses outside the semiconductor industry could do
that.

I started work there in the autumn of 1977 as part of SBS
(Small Business System) team, most of us newcomers, to develop a new
office phone system or PABX. Unlike previous
Post Office systems this was to have electronic terminals with
programmable keys and "lamps" (LEDs). It was to
be controlled by a central computer, which we were going to build
from one of these new microprocessors (the Intel 8085 and Zilog Z80
were then the state of the art) - more on this later!

After we built a demonstration system, using standard parts and a
Signetics 2650 micro, work started on the real thing. I was given the
task of
designing a chip which flashed the LEDs. Since a phone terminal could
have 30 or more of these LEDs and the power consumed by the terminal
had to be kept low, then the LEDs had to be stacked with as many as
possible
in series so that the current could be re-used. Now it so happened that
the IC process we used then was PMOS
(PMOS transistors were easier to build
consistently than NMOS) and the supply voltage
could be 17V.
We would run these chips from +5 and -12V supplies, which at least
allowed a fairly straightforward interface to TTL
and other logic parts running from 5V. So we could have a stack of 6
LEDs. Each LED would have a PMOS
switch
across it which would shunt the current if the LED
was to be off.

Designing the analogue stuff was all done by hand, with simulation
being done as a final verification. At first we used an in-house
simulator called Philpac (by now we had become part of the Philips
empire); only later did we move to Spice. Simulations were run on a
remote computer
using a 75 baud teleprinter terminal! So you took care to get things
right
first time. Schematics were drawn on paper and netlists generated
manually
- a far cry from today's environment. Now the logic design was
interesting, because we used a form of synchronous dynamic logic called
four-phase, which did not need much black magic to get right.